1. Technical Field
The invention relates to vibration damping devices which develop damping performance when applied between two moving members such as automobile suspensions or other equipment. More particularly, the invention relates to a damping device using an electrorheological (ER) fluid as the damping medium which uses two piston-rod guide-assemblies for supporting both ends of the piston rod an positioned so the sliding surfaces are not immersed in the ER fluid and are external to the working chamber of the damper.
2. Background Information
In automotive vehicles, vibrations are caused by traveling over road protrusions or depressions and are transmitted from the tire surface to the vehicle frame. Vibration damping devices have been used to dampen these road vibrations and provide a smoother ride in automotive systems. These shock absorbers are typically oil-filled or high-pressure gas-filled damping devices.
Although conventional oil and high-pressure gas damping devices have proven satisfactory, a more recent development has evolved in which an electrorheological or electroviscous fluid is used within the chamber of the damping device. The liquid is in contact with one or more electrodes, usually mounted in a restrictive passage, which depending upon the size of the electrodes and the amount of voltage applied to the liquid, will change the viscosity of the liquid, enabling the damping device to have an adjustable range of damping characteristics.
Typical automobile dampers, be they electrorheological (ER) dampers or conventional dampers, are axially slidable devices that produce a resistive (damping) force as they are compressed or extended. In practical use they are subjected to, and must be able to withstand, bending forces (side-loads) while retaining axial motion. This necessitates that the slidable members be interconnected at a minimum of two sliding bearing-points. In a conventional damper the slidable members are the damper body or housing and the piston/rod assembly. The corresponding bearing points are the rod-guide assembly and the main piston.
The electrorheological fluids used in ER dampers are most often particle/liquid suspensions. In order to function properly the particles must remain physically intact for the service life of the device. Many known ER dampers are constructed similar to conventional dampers described above, that is the piston is one bearing point and the piston rod the second bearing point. This construction may result in a situation which compromises the integrity of the particles in the ER fluid since one of the bearing points is immersed in the ER fluid. As the damper is cycled, the sliding/rubbing motions of the immersed bearing point subject the particles to forces that may be large enough to damage them. The addition of a bending or side-load force only exacerbates the situation. Should the particles used in the ER fluids be abrasive, the sliding/rubbing motions of the bearing point would erode the metal of the damper body. The resulting inclusion of metallic wear debris in the ER fluid is known to degrade the fluid""s performance.
Examples of various prior art dampers using ER fluids are shown in U.S. Pat. Nos. 5,522,481; 5,590,745; 5,598,908; 5,259,487. In these structures the piston is supported at only one end and thus it provides a rubbing action against the inner surface of the piston housing within the ER fluid. Furthermore, the piston rod is only supported at one end with the piston itself being the other space support.
U.S. Pat. No. 5,513,730 shows a usual type of hydraulic damper in which the piston rod is supported at opposite ends of the piston to counteract any unequal loading on the piston and piston rod. However, the sliding surfaces between the piston rod and fixed bearing members in this dual supported shock absorber are exposed to the fluid, which is not a problem when used with standard hydraulic fluids. However, if such a construction is used with an ER fluid, it results in the undesirable abrasion at the sliding surfaces. Thus, the need exists for a simple and effective ER damper that provides spaced supports to the piston to eliminate unequal forces exerted on the piston and/or piston rod, and most importantly avoids contact between the sliding-contact surfaces and the ER fluid contained within the fluid chamber.
Objectives of the invention include providing an improved damping device using ER fluids, preferably of the type suitable for a vehicle suspension system, which solves the aforementioned problems of prior art dampers by reducing the complexity of the damper without sacrificing the damping characteristics achieved thereby, and which is able to withstand the various loads and forces exerted thereon when mounted between spaced components in a vehicle suspension system.
A further objective of the invention is to provide a damping device that incorporates a pressurized gas reservoir within the damper to prevent cavitation and the formation of bubbles within the ER fluid thereby preventing the creation of electrical arcing within the fluid.
Another objective of the invention is to provide such a damping device suitable for automotive and industrial applications which utilizes the electrorheological fluids or magneto rheological fluids as the damping medium and which uses two spaced piston rod guide and bearing assemblies, both being positioned such that they are not immersed in the damping fluid and are external to the working chamber of the damper to prevent physical contact with the ER or MR damping fluid.
A further objective of the invention is to provide such an ER damping device which has very few moving parts and is therefore less expensive to construct and is extremely reliable.
A still further objective of the invention is to provide such an ER damping device in which the internal piston does not contact the damper body and thus can be used as the positive electrode to activate the ER fluid with the damper body acting as the ground electrode thereby allowing the positive electrode to be physically separated from the vehicle occupants or service personnel to provide a safer damping device.
Another objective of the invention is to provide such a damping device which is similar in many respects to conventional tube-type dampers as to size and means of attachment to the vehicle thereby enabling the damping device to be utilized in existing spaces intended for conventional type dampers, yet which is able to withstand greater side loading forces than heretofore believed possible with conventional dampers having only a single slide support for the piston rod.
A further objective of the invention is to provide such a damping device which is of a rugged, compact, relatively lightweight, simple design which achieves the stated objectives in a simple and efficient manner.
These objectives and advantages are obtained by the improved ER damping device of the present invention, the general nature of which may be stated as including a housing having first and second ends that form an internal fluid chamber; an axially movable piston within the housing and the fluid chamber and dividing said chamber into two separate fluid subchambers; a fluid transfer duct formed between said housing and piston providing fluid transport between said fluid subchambers on opposite sides of said piston, said fluid subchambers adapted to be filled with an electrorheological (ER) fluid; an electrode attached to one of the housing and piston for applying an electric field across at least a portion of the fluid transfer duct to increase the flow resistance of the ER fluid passing therethrough; a piston rod having first and second ends connected to the piston and extending beyond opposite ends of said piston with the first end of said piston rod being adapted to be connected to a first support structure; connection means mounted on the second end of the housing for connecting said second end of the housing to a second structure spaced from the first structure, whereby load on said damping device is supported by said housing and piston rod; first and second piston-rod guide-assemblies mounted adjacent respective ends of the housing and slidably supporting the first and second ends, respectively of the piston rod therein, said first guide assembly having a slide bushing formed with a bore for slidably receiving and supporting the first end of the piston rod therein and an elastomeric seal surrounding the piston rod and located between said slide bushing and the piston chamber to seal said slide bushing from contact with the ER fluid.